This application relates to an electrochemical apparatus for the detection of analytes, and particularly glucose, in blood or interstitial fluid.
Glucose monitoring is a fact of everyday life for diabetic individuals, and the accuracy of such monitoring can literally mean the difference between life and death. To accommodate a normal life style to the need for frequent monitoring of glucose levels, a number of glucose meters are now available which permit the individual to test the glucose level in a small amount of blood. Many of these meters detect glucose in a blood sample electrochemically, by detecting the oxidation of blood glucose using an enzyme such as glucose oxidase provided as part of a disposable, single-use electrode system. Examples of devices of this type are disclosed in European Patent No. 0 127 958, and U.S. Pat. Nos. 5,141,868, 5,286,362, 5,288,636, and 5,437,999 which are incorporated herein by reference.
To use these meters, the user pricks a finger or other body part to produce a small sample of blood or interstitial fluid which is then transferred to the disposable electrode system. This can cause problems, because of the need to take several measurements a day. The biggest drawback to routinely drawing small blood samples is the pain inflicted by the currently available lancets or finger-sticking devices. The most favored site of sampling is the rich capillary bed of the skin of the finger tip which readily yields a drop of blood from a small cut. The finger tip is also rich in pain receptors, and the pain is increased when the incision is too deep, or is too close to a recent incision, or is not deep enough requiring an additional incision. The pain maybe also be increased if the cutting blade penetrates slowly or is withdrawn slowly. Furthermore, the user may be forced to make a larger incision than is necessary in order to get a drop of blood to form for transfer to the measuring strip. Because of this, different designs for lancing devices have been proposed which are designed to facilitate use of the device and limit the pain associated with the procedure. Examples of lancing devices are described in U.S. Pat. Nos. 4,924,879, 5,201,324, 5,318,584, 5,879,311, and 5,879,367 which are incorporated herein by reference.
International Patent Publication No. WO95/10223 describes a device for collection of interstitial fluid. The device can include a membrane on which sample is collected and dried. This membrane is then transferred to an external device for analysis.
Each of these known devices for the electrochemical monitoring of glucose by a diabetic involves a two-step process, in which the skin is first pierced to obtain a sample and this sample is transferred to a sensor for analysis. This presents several drawbacks. First, the user must transfer blood into the detection apparatus which requires a measure of dexterity to align the drop of blood on the finger with the sample-receiving opening of the sensor or meter. Second, because of this transfer, the amount of blood or fluid extracted from the patient may be inappropriate for the sensor, either being too little to provide an accurate measurement or too much, which can increase the amount of pain associated with the procedure.
U.S. Pat. No. 4,637,403 discloses a self-contained device for lancing and testing blood glucose using colorimetry. U.S. Pat. No. 5,054,499 discloses a colorimetric device in which a lancet punctures an absorbent member which includes reagents for the colorimetric detection of glucose prior to puncturing the skin. U.S. Pat. Nos. 5,682,233 and 5,823,973 disclose a sampling device which is sized to allow it to be mated with a testing apparatus for optical analysis of a sample. U.S. Pat. No. 5,746,217 discloses a lancet in which a capillary tube is used to capture sample, which is there analyzed by infrared spectroscopy in the capillary. U.S. Pat. No. 5,879,310 discloses a device in which a lancet punctures the skin and the sample resulting sample of body fluid is transported for analysis in an optical system.
U.S. Pat. No. 4,953,552 discloses a device for electrochemical glucose detection in which reagents for generating the electrochemical signal are coated directly onto the lancet, and thus come into contact with the sample without further user intervention. In this device, there is no spring action to drive the needle, and the needle is simply pressed in by the user. This makes control of the puncture difficult. Furthermore, replacement of the lancet and reagent are inconvenient in the device as disclosed, and mass production of sensors would be difficult.
Thus, there remains room for improvement in the manner in which fluid samples are collected and analyzed.
The present invention provides an improved apparatus for detection and quantitation of an electrochemically-detectable analyte, such as glucose, in blood or interstitial fluid. The apparatus comprises a meter unit, a lancet and an electrochemical sensor. Of these components, the meter is preferably reusable, while the lancet and the electrochemical sensor are preferably intended for single-use.
The meter unit comprises a housing, means disposed within the housing for engaging a lancet and moving an engaged lancet, a connector disposed within the housing for engaging an electrochemical sensor specific for the analyte and transmitting a signal indicative of the amount of analyte, and a display operatively-associated with a connector for displaying the amount of the analyte to user. The electrochemical sensor is adapted for detection of a particular analyte. In addition, the electrochemical sensor comprises an absorptive member for uptake of a sample of blood or interstitial fluid. In one embodiment of the invention, when a lancet is engaged in the apparatus, the means for engaging and moving the lancet moves the lancet from a initial position to a piercing position in which skin of the user is pierced and optionally back to a retracted position, which may be the same as or different from the initial position. The electrochemical sensor is disposed such that the absorptive member takes up a sample from the pierced skin of the user when it is pierced by the lancet without movement of the apparatus. In an alternative embodiment, the lancet is a hollow cannula through which blood or interstitial fluid is transported from the puncture site to an absorbent portion of the electrochemical sensor. Thus, in either embodiment, the invention provides an apparatus with single-step operation in which sample acquisition and analysis occur as a result of the single action of pressing the apparatus against the users skin.
Another aspect of the invention relates to disposable sensor assemblies for use in a meter in accordance with the invention. Such disposable sensor assemblies may contain just the sensor in a support suitable for attachment to the meter or both the sensor and the lancet. In the latter case, the disposable sensor assembly may contain one sensor and one or more lancets, or it may contain a plurality of lancet/sensor pairs.